A DHC8 CREW; TAXIING FOR TKOF AT PHL; TAXIED PAST THE HOLD SHORT FOR THEIR TKOF RWY.

Narrative

WE WERE TAXIING SBOUND ON TXWY E APCHING THE XING TXWY K. WE HAD BEEN INSTRUCTED TO CONTACT TWR FOR A RWY 35 AT TXWY K DEP. I CALLED TWR AND INDICATED WE WERE READY FOR TKOF. AS WE TURNED THE CORNER TO HOLD SHORT OF RWY 35 AT TXWY K; THE TWR CTLR KEYED HIS MIKE; STATED OUR CALL SIGN; PAUSED FOR A MOMENT (APPROX 2 SECONDS); AND ASKED US TO HOLD SHORT. THE CAPT HAD NOT STOPPED AT THE HOLD SHORT LINE DURING THE PAUSE; I ASSUME BECAUSE HE EXPECTED A TKOF CLRNC; SO WE WERE AT THAT POINT 1/2 WAY ACROSS THE HOLD SHORT LINE. I LOOKED AT THE APT AND SAID 'HE SAID HOLD SHORT.' APPROX 5 SECONDS PASSED AND THE CTLR CLRED US FOR TKOF. THE CTLR NEVER MENTIONED OUR INCURSION; SO HE MIGHT NOT HAVE SEEN US CROSS THE HOLD LINE. THE CAPT'S EXPECTATION FOR A TKOF CLRNC WAS THE CAUSAL FACTOR IN MY OPINION. UNTIL YOU HEAR 'CLRED FOR TKOF' NO PART OF THE AIRPLANE SHOULD PENETRATE THE VERT PLANE OF THE HOLD SHORT LINE. KNOWING THIS I COULD HAVE STOMPED ON THE BRAKES THE MOMENT THE CTLR PAUSED. IT WAS A SPLIT SECOND DECISION. WE WERE BOTH WELL RESTED AND NUTRITIONALLY HEALTHY SO IN MY OPINION THERE WAS NO MENTAL OR PHYSICAL IMPAIRMENT.